1. Field of the Invention
The present invention relates to a method of dividing a wafer.
2. Description of the Related Art
A wafer having a plurality of devices which are formed at a surface side and partitioned by streets is formed to be a certain thickness by grinding a back surface, and then subjected to cutting along the streets and, thereby divided into individual devices for use in various electronic instruments.
However, there has been a problem that since such cutting is performed by crushing the streets using a cutting blade rotated at high speed, the blade containing grinding particles such as diamond particles hardened by nickel plating and the like and being formed to be approximately 20 μm in thickness, therefore small chips appear on a cutting surface (side face) of the device, which reduces die strength of the device. In particular, when the thickness of the wafer is decreased to 100 μm or less, or further decreased to 50 μm or less, the problem is more significant.
Japanese Patent Application JP2004293693 discloses a technique wherein a resist film is coated on a back surface of a wafer, then the resist films in areas corresponding to the streets are removed, and then the areas corresponding to the streets are diced by using plasma etching, thereby the wafer is divided into individual devices. A technique of wafer dicing by etching is also disclosed, for example, in JP-A-2002-93752.
However, the wafer dicing by etching essentially needs a resist film for preventing etching of a device area, but the resist film firmly adheres to backs of the devices. Therefore, the resist film cannot be easily separated and, consequently, must be ashed, causing reduction in productivity.